;
; Copyright © 2016 Keith Packard <keithp@keithp.com>
;
; This program is free software; you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, either version 2 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful, but
; WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
; General Public License for more details.
;
; Lisp code placed in ROM

					; return a list containing all of the arguments

(set (quote list) (lexpr (l) l))

					;
					; Define a variable without returning the value
					; Useful when defining functions to avoid
					; having lots of output generated
					;

(set (quote define) (macro (name val rest)
			(list
			 'progn
			 (list
			  'set
			  (list 'quote name)
			  val)
			 (list 'quote name)
			 )
			)
     )

					;
					; A slightly more convenient form
					; for defining lambdas.
					;
					; (defun <name> (<params>) s-exprs)
					;

(define defun (macro (name args exprs)
		  (list
		   define
		   name
		   (cons 'lambda (cons args exprs))
		   )
		  )
     )

					; basic list accessors


(defun cadr (l) (car (cdr l)))

(defun caddr (l) (car (cdr (cdr l))))

(defun nth (list n)
  (cond ((= n 0) (car list))
	((nth (cdr list) (1- n)))
	)
  )

					; simple math operators

(defun 1+ (x) (+ x 1))
(defun 1- (x) (- x 1))

(define zero? (macro (value rest)
		     (list
		      eq?
		      value
		      0)
		     )
  )

(zero? 1)
(zero? 0)
(zero? "hello")

(define positive? (macro (value rest)
			 (list
			  >
			  value
			  0)
			 )
  )

(positive? 12)
(positive? -12)

(define negative? (macro (value rest)
			 (list
			  <
			  value
			  0)
			 )
  )

(negative? 12)
(negative? -12)

(defun abs (x) (cond ((>= x 0) x)
		     (else (- x)))
       )

(abs 12)
(abs -12)

(define max (lexpr (first rest)
		   (while (not (null? rest))
		     (cond ((< first (car rest))
			    (set! first (car rest)))
			   )
		     (set! rest (cdr rest))
		     )
		   first)
  )

(max 1 2 3)
(max 3 2 1)

(define min (lexpr (first rest)
		   (while (not (null? rest))
		     (cond ((> first (car rest))
			    (set! first (car rest)))
			   )
		     (set! rest (cdr rest))
		     )
		   first)
  )

(min 1 2 3)
(min 3 2 1)

(defun even? (x) (zero? (% x 2)))

(even? 2)
(even? -2)
(even? 3)
(even? -1)

(defun odd? (x) (not (even? x)))

(odd? 2)
(odd? -2)
(odd? 3)
(odd? -1)

(define exact? number?)
(defun inexact? (x) #f)

					; (if <condition> <if-true>)
					; (if <condition> <if-true> <if-false)

(define if (macro (test args)
	       (cond ((null? (cdr args))
		      (list
		       cond
		       (list test (car args)))
		      )
		     (else
		      (list
		       cond
		       (list test (car args))
		       (list 'else (cadr args))
		       )
		      )
		     )
	       )
     )

(if (> 3 2) 'yes)
(if (> 3 2) 'yes 'no)
(if (> 2 3) 'no 'yes)
(if (> 2 3) 'no)

					; define a set of local
					; variables and then evaluate
					; a list of sexprs
					;
					; (let (var-defines) sexprs)
					;
					; where var-defines are either
					;
					; (name value)
					;
					; or
					;
					; (name)
					;
					; e.g.
					;
					; (let ((x 1) (y)) (set! y (+ x 1)) y)

(define let (macro (vars exprs)
		((lambda (make-names make-exprs make-nils)

					;
					; make the list of names in the let
					;

		   (set! make-names (lambda (vars)
				      (cond ((not (null? vars))
					     (cons (car (car vars))
						   (make-names (cdr vars))))
					    )
				      )
			 )

					; the set of expressions is
					; the list of set expressions
					; pre-pended to the
					; expressions to evaluate

		   (set! make-exprs (lambda (vars exprs)
				      (cond ((not (null? vars)) (cons
						   (list set
							 (list quote
							       (car (car vars))
							       )
							 (cadr (car vars))
							 )
						   (make-exprs (cdr vars) exprs)
						   )
						  )
					    (exprs)
					    )
				      )
			 )

					; the parameters to the lambda is a list
					; of nils of the right length

		   (set! make-nils (lambda (vars)
				     (cond ((not (null? vars)) (cons () (make-nils (cdr vars))))
					   )
				     )
			 )
					; prepend the set operations
					; to the expressions

		   (set! exprs (make-exprs vars exprs))

					; build the lambda.

		   (cons (cons 'lambda (cons (make-names vars) exprs))
			 (make-nils vars)
			 )
		   )
		 ()
		 ()
		 ()
		 )
		)
     )

(let ((x 1)) x)

					; boolean operators

(define or (lexpr (l)
	       (let ((ret #f))
		 (while (not (null? l))
		   (cond ((car l) (set! ret #t) (set! l ()))
			 ((set! l (cdr l)))))
		 ret
		 )
	       )
     )

					; execute to resolve macros

(or #f #t)

(define and (lexpr (l)
	       (let ((ret #t))
		 (while (not (null? l))
		   (cond ((car l)
			  (set! l (cdr l)))
			 (#t
			  (set! ret #f)
			  (set! l ()))
			 )
		   )
		 ret
		 )
	       )
     )

					; execute to resolve macros

(and #t #f)


(define append (lexpr (args)
		      (let ((append-list (lambda (a b)
					   (cond ((null? a) b)
						 (else (cons (car a) (append-list (cdr a) b)))
						 )
					   )
					 )
			    (append-lists (lambda (lists)
					    (cond ((null? lists) lists)
						  ((null? (cdr lists)) (car lists))
						  (else (append-list (car lists) (append-lists (cdr lists))))
						  )
					    )
					  )
			    )
			(append-lists args)
			)
		      )
  )

(append '(a b c) '(d e f) '(g h i))

(defun reverse (list)
  (let ((result ()))
    (while (not (null? list))
      (set! result (cons (car list) result))
      (set! list (cdr list))
      )
    result)
  )

(reverse '(1 2 3))

(define list-tail
  (lambda (x k)
    (if (zero? k)
	x
      (list-tail (cdr x) (- k 1)))))

(list-tail '(1 2 3) 2)
					; recursive equality

(defun equal? (a b)
  (cond ((eq? a b) #t)
	((and (pair? a) (pair? b))
	 (and (equal? (car a) (car b))
	      (equal? (cdr a) (cdr b)))
	 )
	(else #f)
	)
  )

(equal? '(a b c) '(a b c))
(equal? '(a b c) '(a b b))

;(define number->string (lexpr (arg opt)
;			      (let ((base (if (null? opt) 10 (car opt)))
					;
;